In our earlier applications we proposed the condensation of hydroxyl (--OH) and carboxylic acid (--COOH) or carboxylic acid halides (--COX) on an aromatic hub having at least three such functionalities. The condensation occurred in a suitable solvent, such as DMAC, under an inert atmosphere in the presence of triethylamine (TEA). We have found that, when reacting, for example, phloroglucinol with an acid chloride end cap of the formula: ##STR1## in DMAC and TEA that the resulting product is a mixture of ##STR2## The condensation is difficult to drive to completion (i.e., replacement of all the --OH groups) to yield the desired product (I). The yield of fully reacted multidimensional ester (I) can be improved, however, by replacing the TEA with thallium ethoxide (T1-OC.sub.2 H.sub.5).
The present invention is a method to improve the yield of fully-substituted multidimensional polyesters, particularly polyester oligomers having a trisubstituted phenylene hub and crosslinking hydrocarbon unsaturation at the end of each arm linked to the hub. The method involves conducting the esterification reaction in the presence of a thallium catalyst, such as thallium ethoxide, in a suitable solvent under an inert atmosphere. Preferably, the solvent includes DMAC and TEA.